Magnetic core multivibrator circuit



' Dec. 6, 1960 R. w. ROCHELLE 2,963,658

MAGNETIC CORE MULTIVIBRATOR CIRCUIT Filed Nov. 1, 1957 I 1151i- :EI. l5l5 3 3 KP KR I6 e I6 I A H I4 '3 l7 E a 5 INVENTOR j 5 ROBERT w.ROCHELLE o 3 E O O Q BASE VOLTAGE B O o o ATTORNEYj nite T MAGNETIC consMULTIVIBRATOR cmcUrr Robert W. Rochelle, 943 Swarthmore Drive, BucknellManor, Alexandria, Va.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

This invention relates to electronic circuits and more particularly to amultivibrator circuit including a magnetic core and transistors.

Reduction of the number of components in a multivibrator has long been agoal in the art. Some prior art multivibrators using magnetic coresrequire many core windings in order to enable the circuit to operateproperly. In other prior circuits, it was either inconvenient orimpossible to wind the necessary turns on the core. In still other priorcircuits, difiiculty is encountered in starting the oscillation of thecircuit.

It is therefore, an object of this invention to provide an efficientmultivibrator composed of a minimum number of components.

Another object is to provide a multivibrator wherein oscillation iseasily started.

A still further object of this invention is to provide a magnetic coremultivibrator requiring only a single winding on the core.

Another object is to provide a magnetic core multivibrator circuitrequiring a small number of winding turns on the core.

These and other features of the invention, as well as additional objectstherefor, will become apparent by reference to the ensuing descriptionand the accompanying drawings in which:

'Fig. 1 is a schematic diagram of an embodiment of the magnetic coremultivibrator circuit of this invention.

Fig. 2 is a schematic diagram of a second embodiment of the circuit ofthis invention.

Fig. 3 is a schematic diagram of a third embodiment of the circuit ofthis invention.

Fig. 4 is a graphic showing of the relationship of the base voltage tothe collector current for the transistors used for switching purposes inthis invention.

In accordance with the basic teachings of the present invention, asimplified multivibrator circuit is provided requiring as essentialelements a coupling transformer, two transistors and a suitablerelatively simple power source. The coupling transformer comprises asingle center tapped Winding placed upon a core composed of highremanence material having square-loop hysteresis characteristics. A corecomposed of such material, which is somewhat similar to a permanentmagnet in certain of its characteristics, can be driven to saturation ineither of two polarities by a suitable driving signal applied to awinding thereon. Upon removal of this driving signal, however, the coredoes not return to an unmagnetized condition, as does ordinarytransformer core material, for

example, but assumes a condition of magnetism some- .what lower thansaturation, called: remanence, which is thereafter retained indefinitelyor until forceably removed by a driving signal of opposite polarity tothat of the original driving signal. It is this slip-back from satu-Statcs Patent f 2,963,658 Fatented Dec. 6, 196 0 ration to remanencethat is employed in a novel way in the circuit of the present inventionto produce the alternate triggering of the transistors to produce thefamiliar multivibrator action.

The invention as shown in Fig. 1 includes a magnetic core 1 with acenter tapped winding thereon. The center tap is connected to thenegative side of power supply 2 through switch 3. The positive side ofthe power supply 2 is connected to a first junction point to which arecon nected the emitters of transistors 9 and 13. The collector oftransistor 9 is connected to junction 11 to which also are connected thedotted end of winding 4, which is onc-half of the center tapped winding,and thebase of transistor 13. p The collector of transistor 13 isconnected to junction 6 to which also are connected the not-dotted endof winding 5, which is the other half of the center tapped winding, andthe base of transistor 9. Also included in the circuit are outputterminals connected across the center-tapped winding on the magneticcore 1.

To better understand the operation of the circuit as shown in Fig. I, itis assumed that core 1 is initially at negative remanence before theapplication of the power from the power source 2. A positive magnetizingforce is needed to change the state of core 1 from negative remanence topositive saturation. By convention, positive current entering a dottedend of a core winding induces positive magnetizing force in the core.The negative side of the power source 2 is applied to the junction ofwind ings 4 and 5 which are halves of a single center tapped Winding.With the core in a condition of negative remanence, winding 4 is capableof changing the core flux alignment to positive saturation. As set forthabove, if the core 1 is initially at negative remanence, when the switch3 is closed, the flux alignment will change toward positive saturation.A negative potential is induced across winding 5 which, combined withthe negative potential of the power source 2, when applied throughjunction 6 to the base of p-n-p transistor 9, causes transistor 9 to beconductive. Current will then flow from the positive side of powersource 2 through transistor 9, junction 11, winding 4 and switch 3 tothe negative side of power source 2. During this current flow throughtransistor 9 and winding 4, core 1 is driven from negative remanence topositive saturation. Transistor switch 13'is held in the off state dueto the fact that the combined potential from the battery 3 and winding 4is not enough for conduction as witnessed by Fig. 4 as discussed below.

When the condition of core 1 reaches positive saturation, the negativepotential induced across winding 5 disappears and transistor switch 9cuts oif. The drop from flux saturation to remanence in the core, uponthe blocking of transistor 9, induces a negative signal-which is appliedto the base of transistor 13. This negative signal turns transistorswitch 13 on and current will then flow from the positive side of powersource 2 through transistor 13, junction 6, winding 5 and switch 3 tothe negative side of power source 2. During this current flow throughtransistor 13 and winding 5, core 1 is driven to negative saturation.

When the condition of core 1 reaches negative saturation, the negativepotential induced across winding disappears and transistor switch 13cuts off. The slipback from saturation to remanence upon the opening oftransistor switch 13 induces a negative signal across winding 5 which isapplied to the base of transistor 9. This negative signal turnstransistor switch 9 on and current will then flow from the positive sideof the power source 2 through transistor switch 9, junction 11, winding4, and switch 3 to the negative side of power source 2. v

As in a typical two state multivibrator, it is seenthat in the firststate, transistor 9 is conductive and tran sistor 13is non-conductive.In the second state, nan.-

sistor 9 is non-conductive and transistor 13 is conductive.

The circuit will continue to operate with the flux alignment of the corebeing reversed automatically by the selective operation of thetransistors until such time that the power source is disconnected fromthe circuit.

A typical output is provided so that an output of square wavecharacteristics can be obtained across terminals 15 and 16.

The circuit shown in Fig. 2 difiers from the circuit of Fig.1 only bythe addition of current limiting resistors 14- and 7. Resistors 14 and 7are added should the values of the components require such resistance tolimit the current that is available to the transistors.

The circuit of Fig. 3 difiers from the circuit of Fig. l by the additionof the current limiting resistors 14 and 7 found also in Fig. 2, by theaddition of the biasing battery 17 which is added to assure that thetransistor which should be non-conductive is completely non-conductive,and by the addition of the voltage divider resistors 8 and 12. Resistors8 and 12 limit the increased biasing current provided by battery 17 toincrease proper switching control.

Fig. 4 shows the relationship of collector current with respect tovoltages applied to the base thereof when the collector load resistanceis constant. The particular curve is the curve of a p-n-p type number2N128 transistor which is typical of the transistors which are usable inthis invention. Pmicular transistors are selected which have valueswhich meet circuit requirements. As the curve in Fig. 4 indicates, asmall amount of current leakage occurs when a voltage is applied to thebase of the transistor. When the voltage applied to the base is in therange between minus 0.2 and 0.3 volt, current will fiow freely throughthe collector of the transistor. The amount of current which will flowreaches a maximum when the base voltage is about minus 0.3 volt as thetransistor will become saturated and can pass no more than said maximumcurrent. It is this built-in bias characteristic of the transistors tomaintain the transistors in the non-conductive condition even though thebase voltage is slightly negative which allows the circuit to operateproperly without the addition of biasing components.

In a typical circuit as shown in Fig. 2, core 1 is made of 79% nickel,4% molybdenum, and the balance is iron. The center tapped winding has atotal of 400 turns. The power source 2 is a 3 volt battery. Thetransistors 9 and 13 are p-n-p type number 2N128 and the resistors 7 and14 are 1,000 ohms each. In Fig. 3, biasing source 17 could be a 1 /2volt battery.

It is obvious that the polarity of the battery can be reversed and n-p-ntransistors can be used.

It is seen that I have provided a very compact and eflicientmultivibrator circuit with a minimum number of components. Themultivibrator of this circuit is very easily set into oscillation. Undersevere loading of the output, the voltage drops across the halves of thecenter tapped winding might, rarely, be equal; however, oscillation canbe started by merely touching one of the halves, or by any means thatwill provided a slight inductive change in one of the halves. Also, inthis multivibrator, the only winding is center tapped, a feature whichminimizes the problems of providing windings on the core.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In a multivibrator, a magnetic core, a winding on said core havingfirst and second ends and a center terminal, a power source includingpositive and negative terminals, means connecting said center terminalto said negative terminal, a first transistor having a collector, a.base and an emitter, a second transistor having a collector, a base andan emitter, means connecting said emitters of said first and said secondtransistors to the said positive terminal, means connecting said firstend of said winding to the collector of said first transistor and to thebase of said second transistor, means connecting said second end of saidwinding to the collector of said second transistor and to the base ofsaid first transistor.

2. In an electronic circuit, a magnetic core, a winding on said corehaving first and second ends and a center terminal, a power sourceincluding first and second terminals, means connecting said centerterminal to said first terminal, a first transistor having a collector,a base and an emitter, a second transistor having a collector, a baseand an emitter, means connecting said emitters of said first and saidsecond transistors to the said second terminal, means connecting saidfirst end of said winding on said core to the collector of said firsttransistor and to the base of said second transistor, means connectingsaid second end of said winding on said core to the collector of saidsecond transistor and to the base of said first transistor.

3. In a multivibrator, a magnetic core, a winding on said core havingfirst and second end connections and a center connection, a power sourceincluding two terminals, means connecting said center connection to oneof said terminals, first and second transistors each having a collector,a base and an emitter, means connecting said emitters to the other ofsaid terminals, means connecting said first end connection at a firstjunction to the collector of said first transistor and the base of saidsecond transistor, and means connecting said second end connection at asecond junction to the collector of said second transistor and the baseof said first transistor.

4. The multivibrator of claim 3 wherein said means for connecting saidfirst end connection at a first junction to the base of said secondtransistor includes a first current limiting resistor and wherein saidmeans for connecting said second end connection at a second junction tothe base of said first transistor includes a second current limitingresistor.

5. The multivibrator of claim 4, circuit divider means including thirdand fourth resistors each having two leads, means connecting one lead ofsaid third resistor between the base of the first transistor and thesecond current limiting resistor, means connecting one lead of saidfourth resistor between the base of the second transistor and the firstcurrent limiting resistor, means connecting said other lead of saidthird and said fourth resistors to a common junction, biasing sourcemeans including third and fourth terminals, means connecting said thirdterinal to said common junction and means connecting said fourthterminal to said means connecting said emitters.

6. In a multivibrator, a magnetic core, a winding on said core havingfirst and second end connections and a center connection, a power sourceincluding positive and negative terminals, means connecting said centerconnection to said negative terminal, a first transistor and a secondtransistor, each of said transistors being of the p-n-p type, eachhaving a collector, a base and an emitter, means connecting said'emitters to said positive terminal, means connecting said first endconnection at a first junction to the collector of said first transistorand the base of said second transistor, and means couneeting said secondend connection at a second junction to the collector of said secondtransistor and the base of said first transistor.

7. The multivibrator of claim 6 wherein said means for connecting saidfirst end connection at a first junction to the base of said secondtransistor includes a first current limiting resistor and said means forconnecting said second end connection at a second junction to the baseof said first transistor includes a second current limiting resistor.

8. The multivibrator of claim 7 including circuit divider comprising tworesistors, one end of a first circuit divider 5 resistor means isconnected to a point between the base of said first transistor andsecond current limiting resistor, one end of a second circuit dividerresistor means is connected between the base of said second transistorand said first current limiting resistor, means connecting the other endof said circuit divider resistors at a third junction, biasing sourcemeans, means connecting said biasing source means to a third junctionand to the means connecting said emitters to the other of saidterminals.

9. In a multivibrator, a magnetic core having rectangular hysteresisloop characteristics, a winding on said core having first and secondends and a center terminal, a power source including positive andnegative terminals, means connecting said center terminal to saidnegative terminal, a first transistor having a collector, a base and anemitter, a second transistor having a collector, a base and an emitter,means connecting said emitter of said first and said second transistorsto the said positive terminal, means connecting said first end of saidwinding to the collector of said first transistor and to the base ofsaid second transistor, means connecting said second end of said windingto the collector of said second transistor and to the base of said firsttransistor.

10. In an electronic circuit, a magnetic core having rectangularhysteresis loop characteristics, a winding on said core having first andsecond ends and a center terminal, a power source including first andsecond terminals, means connecting said center terminal to said firstterminal, a first transistor having a collector, a base and an emitter,a second transistor having a collector, a base and an emitter, meansconnecting said emitters of said first and said second transistors tothe said second terminal, means connecting said first end of saidwinding on said core to the collector of said first transistor and tothe base of said second transistor, means connecting said second end ofsaid winding on said core to the collector of said second transistor andto the base of said first transistor.

11. In a multivibrator, a magnetic core having rectangular hysteresisloop characteristics, a winding on said core having first and second endconnections and a center connection, a power source including twoterminals, means connecting said center connection to one of saidterminals, first and second transistors each having a collector, a baseand an emitter, means connecting said emitters to the other of saidterminals, means connecting said first end connection at a firstjunction to the collector of said first transistor and the base of saidsecond transister, and means connecting said second end connection at asecond junction to the collector of said second transistor and the baseof said first transistor.

12. In a multivibrator, a magnetic core having rectangular hysteresisloop characteristics, a winding on said core having first and second endconnections and a center connection, a power source including positiveand negative terminals, means connecting said center connection to saidnegative terminal, a first transistor and a second transistor, each ofsaid transistors being of the p-n-p type, each having a collector, abase and an emitter, means connecting said emitters to said positiveterminal, means connecting said first end connection at a first junctionto the collector of said first transistor and the base of said secondtransistor, and means connecting said second end connection at a secondjunction to the collector of said second transistor and the base of saidfirst transistor.

References Cited in the file of this patent UNITED STATES PATENTS2,733,384 Bright et al Feb. 26, 1957 2,826,731 Paynter Mar. 11, 19582,837,651 Schultz June 3, 1958 2,849,614 Royer et al. -e Aug. 26, 19582,912,653 Tillman Nov. 10, 1959 Disclaimer 2,963,658.R0be1't W.Rochelle, Alexandria, Va. MAGNETIC CORE MULTI- VIBRATOR CIRCUIT. Patentdated Dec. 6, 1960. Disclaimer filed Mar. 22, 1963, by the inventor.Hereby enters this disclaimer to claims 2 and 10 of said patent.

[Ofiicial Gazette September 3, 1963.]

Disclaimer 2,963,658.R0be7=t W. Rochelle, Alexandria, Va. MAGNETIC ComaMULTI- VIBRATOR CIRCUIT. Patent dated. Dec. 6, 1960. Disclaimer filedMar. 22, 1963, by the inventor. Hereby enters this disclaimer to claims2 and 10 of said patent.

[Ojfioial Gazette September 3, 1963.]

